Such droplet dispensing devices, as those of the present invention, are also sometimes called atomizers, nebulizers and the like. They normally contain a nozzle body on a support part, in particular, a nozzle body of a liquid droplet spray device which dispenses a liquid substance as a liquid droplet spray from the device through the nozzles of the nozzle body. They further consist of an actuator based on a vibrating element which generally causes the liquid to vibrate, to be accelerated and expelled as droplets. They further consist of elements such as liquid space, liquid feed and fluid interface to a reservoir, a reservoir as well as electrical connections between the vibrating element and a corresponding electronic circuitry. Such elements may be contained in the aforementioned support part, in a further support part or they may be contained in a number of support parts. The liquid may be for example an ambient fragrance, a perfume, an insecticide, a liquid pharmaceutical formulation, aqueous based liquids and flammable or combustible liquids.
Such nozzle bodies are sometimes called aperture plates, nozzle arrays, dosing apertures, orifice plates, vibratable membrane members, dosing aperture arrangements, aerosol generators and the like. These terms are hence to be understood as being interchangeable throughout the present document.
Such nozzle bodies and droplet spray devices are well known as such. For example, the document WO2007/062698, in the name of the present Applicant, describes a liquid droplet spray device having a top substrate formed of a main body and of a nozzle body. The nozzle body contains a nozzle array of liquid droplet outlet means allowing a liquid substance contained in the liquid droplet spray device to exit the device, in this case as a spray of droplets. Liquid may be supplied from a replaceable reservoir by way of a wick using capillary flow. Generally, the reservoir is a dispensable refill that needs to be replaced regularly.
The document U.S. Pat. No. 7,017,829 describes a liquid droplet spray device having a wicking apparatus with a wick for use in a replaceable reservoir assembly that contains liquid to be atomized by a vibratory aperture plate configured to dispense the liquid from the reservoir assembly through the orifices of the vibratory plate. In this device, the wick must contact the vibratory plate to allow for capillary flow of liquid from the reservoir to the plate for ejection of the liquid.
Thus, in order to ensure capillary flow, typically, the wick is too long, so that any fabrication tolerance, which might lead to a wick that would be too short, will be overcompensated.
Furthermore, in order to obtain an acceptable draining ratio of the reservoir, the wick should fully contact the inner bottom surface of the reservoir for it to be capable to substantially drain and empty the reservoir. Indeed, if the wick does not reach the plate, no spray can be generated or ejected.
To ensure such contact, again, the wick is typically over-sized so as to compensate for manufacturing tolerances.
However, when a wick that is too long than actually designed is inserted into the reservoir, and positioned below the orifice plate, the wick will inevitably be compressed against the plate and against the inner bottom surface of the reservoir. This compression of the wick then leads to unreliable priming and irregular ejection of liquid each time a reservoir is changed.
In fact, by compressing the wick, which is thus forced into contact to the plate, a so-called squeezing effect is obtained which leads to an increased flow rate of liquid when the wick is first inserted into a replacement reservoir. However, after a certain moment in time, as shown by curve a in FIG. 1, the wick and plate assembly will stabilize in the new position and the flow rate will drop from the increased rate to the intended rate.
Clearly, this is highly undesirable for a consumer, as s/he will have to adjust and re-adjust the flow rate each time the reservoir is replaced in order to have a constant flow rate over time.
Document WO 2005/097349 describes a similar liquid droplet spray device with a wicking apparatus. The wick is formed of two different materials with a rigid main section and a compliant top section. The top compliant section is thus compressible and is pressed into contact with the vibratory orifice plate to allow liquid to flow from the reservoir to the plate by capillary action, and may then be expelled.
Thus, again, the wick is compressed against the plate thus resulting in a squeezing effect, albeit more moderate as compared with the previous document mentioned above, so that here too, an unstable flow rate will occur when inserting a new reservoir.
As for the draining ratio, in this device the rigid main section of the wick would also have to be longer than designed to compensate for manufacturing tolerances and to ensure a full contact with the inner bottom surface of the reservoir.
It is also known to use wick holders so as to correctly and/or securely fix a wick in a reservoir. For example, the document U.S. Pat. No. 6,896,196 describes a liquid droplet spray device with a wicking apparatus that has a wick holder 8 for receiving a wick. The holder is positioned onto a reservoir's bottleneck, and holds the wick in place by way of clamping fingers so as to allow for easy insertion of the wick into the reservoir, while at the same time preventing accidental removal of the wick. However, this document is silent about flow rate or draining ratios.
In view of the above, it is an object of the present invention to provide an innovative wicking apparatus for a droplet spray device that overcomes the inconveniences presented by the prior art documents.